There are so many coins, but many of them just a copy of anothers. Why they waste their time for nothing?

Its not a waste of time, you did not really know the essence of business, developers are creating coins to get profit and because of that, ico's are being made to be promoted and earn investors. In this way those developers will have profit from their created coin and grow its value in the market at the time goes by.
Simple, once their coins/tokens is getting high and so expensive. They'll dump it and gone. That's was mostly happened. Crypto world so poisoned by those developers.